1. Field of the Invention
The present invention relates to an electronic component having a capacitor element.
2. Description of the Related Art
On an internal circuit of electronic appliances such as a personal computer and a cellular telephone, various surface mount electronic components are mounted. For the surface mount electronic component, thin film electronic components are known that are formed using thin film formation technique.
For thin film electronic components, a thin film capacitor, a thin film inductor, a thin film LC composite component, a thin film lumped constant device, a thin film distributed constant device and a thin film multilayer composite component are named. In addition, for composite components having a capacitor, a low pass filter (LPF), a high pass filter (HPF), a bandpass filter (BPF) which passes only signals in a predetermined frequency range and attenuates signals in the other frequency ranges, a trap filter which removes signals in a predetermined frequency range, and so on are named. In addition, for the other electronic components that combine them, a diplexer, a duplexer, an antenna switch module, an RF module and so on are named.
For electronic components for use in frequencies of 500 MHz or above, particularly for high frequencies of microwave frequency bands (GHz bands), it is demanded to realize reductions in size, thickness and costs. With regard to the thin film electronic components having a capacitor element, reductions in the electrode area and the number of layers of dielectric films of the capacitor element greatly affect reductions in size, thickness, and costs and the realization of high frequency of the electronic component. In the capacitor element for use in high frequencies, a dielectric film of a high dielectric material is used, or the film thickness of the dielectric film is decreased to intend the reduction in the electrode area of the capacitor element and to intend reductions in size, thickness, and costs and the realization of high capacitance. Moreover, the dielectric film is multilayered to intend the realization of high capacitance of the capacitor element.
FIGS. 35A and 35B show the schematic configuration of a conventional thin film capacitor element 411. FIG. 35A shows a plan view depicting the capacitor element 411, and FIG. 35B shows a diagram depicting a cross section cut at line A-A shown in FIG. 35A. As shown in FIGS. 35A and 35B, the capacitor element 411 has a lower conductor 421 which is formed on a substrate 51, a dielectric film 431 which is formed on the lower conductor 421, and an upper conductor 423 which is formed on the dielectric film 431. Portions of the lower conductor 421 and the upper conductor 423 function as the electrodes of the capacitor element 411.
The capacitance value of the capacitor element 411 is defined by an area (electrode area) that the upper conductor 423 and the lower conductor 421 are faced to each other, and a film thickness d and the dielectric constant of the dielectric film 431. The electrode area that is one factor defining the capacitance value of the capacitor element 411 is defined by an area l1×l2 of the dielectric film 431, the area is sandwiched between the lower conductor 421 and the upper conductor 423.
The dielectric film 431 covers the top and the end part of the lower conductor 421. The film thickness of the dielectric film 431 tends to be thinner at the end part of the lower conductor 421 (in FIG. 35B, the film thickness f) than the top of the lower conductor 421 (in FIG. 35B, the film thickness d). When the dielectric film 431 is formed in a thin film, at the end part of the lower conductor 421, the dielectric film 431 might not be formed on the lower conductor 421. Thus, the insulating properties between the lower conductor 421 and the upper conductor 423 are not sufficiently obtained at the end part of the lower conductor 421, and short circuit defects tend to occur. Therefore, a problem arises that the breakdown limit of the withstand voltage of the capacitor element 411 drops to cause the unstable quality between products against electric power. Short circuit defects and a reduction in the breakdown limit of the withstand voltage tend to occur when the film thickness d of the dielectric film 431 is thinner than the thickness of the lower conductor 421 and the upper conductor 423, and when the end part shape of the lower conductor 421 is in a reverse taper.
Therefore, in the capacitor element 411, a material of high insulating properties is used for the dielectric film 431, or the film thickness d of the dielectric film 431 is thickened to intend the improvement of dielectric voltage. However, when the film thickness d of the dielectric film 431 is thickened, it is necessary to increase the electrode area l1×l2 of the capacitor element 411 in order to obtain high capacitance, causing another problem that it is difficult to reduce the size of the electronic component having the capacitor element 411.
In addition, the accuracy of the capacitance value of the capacitor element 411 is affected by the accuracy of the relative positions between the lower conductor 421 and the upper conductor 423, the accuracy of the shape of the lower conductor 421 or the upper conductor 423, the accuracy of the film thickness and the dielectric constant of the dielectric film 431, the surface roughness of the lower conductor 421 and the upper conductor 423, etc.
However, the capacitor element 411 has a problem that when it is reduced in size, the accuracy of the relative positions between the lower conductor 421 and the upper conductor 423 drops, and it is difficult to obtain the capacitance value highly accurately. Moreover, in order to consider equivalent series resistance (ESR) and parasitic inductance, in the cases in which the set film thickness of the lower conductor 421 is thick, and in which the wiring length of the lower conductor 421 is long, the capacitance value of the capacitance formed between the end part of the lower conductor 421 and the upper conductor 423 becomes large, and the unevenness of the film thickness f of the dielectric film 431 covering the end part of the lower conductor 421 adversely affects a desired capacitance value.
In addition, in the electronic component having the capacitor, the circuit layout is adjusted so that the distance between the conductor of the capacitor element 411 and the terminal is reduced and a lead conductor that connects the capacitor element 411 to the circuit device adjacent to the capacitor element 411 is shortened, whereby it is intended to reduce parasitic inductance and stray capacitance.
However, since a part of the lead conductor contacts with the dielectric film 431, the capacitance value of the capacitor element 411 is different from the design value when the positions of forming the lower conductor 421 and the upper conductor 423 are shifted. In order to reduce a shift of the capacitance value of the capacitor from the design value, for example, the width of the lead conductor is formed narrow. Since the width of the lead conductor is formed narrow to increase parasitic inductance, problems arise that the high frequency characteristics of the electronic component are degraded, and that the transmission loss becomes large.
FIG. 36 shows a cross section depicting a thin film capacitor element 1011 disclosed in Patent Reference 1. As shown in FIG. 36, the thin film capacitor element 1011 has a lower electrode 1021 and a dielectric layer 1031 in turn laminated on a substrate 51 in which the rim part of the dielectric layer 1031 is covered with an insulating layer 1033 having an aperture 1033a, and an upper electrode 1023 formed on the insulating layer 1033 is laminated on the dielectric layer 1031 in the aperture 1033a. With this configuration, since the insulating layer 1033 covering the rim part of the dielectric layer 1031 surely insulates the lower electrode 1021 from the upper electrode 1023, drops and fluctuations in the breakdown voltage caused by the coverage defect of the dielectric layer 1031 can be surely prevented. In addition, since the aperture of the insulating layer 1033 defines the capacitance value of the capacitor, the variations in the capacitance value can be decreased regardless of the accuracy of the size and alignment of the lower electrode 1021 with the upper electrode 1023.
However, in the thin film capacitor element 1011 disclosed in Patent Reference 1, since the upper electrode 1023 is also formed in the same layer as the lower electrode 1021 and faced thereto through the insulating layer 1033, parasitic capacitance (stray capacitance) occurs between the side part of the lower electrode 1021 and the upper electrode 1023. Since the insulating layer 1033 becomes thinner as the thin film capacitor element 1011 is reduced in size, the ratio of the parasitic capacitance to the capacitance value of the thin film capacitor element 1011 becomes large. In addition, since the insulating layer 1033 has a shape that protrudes toward the surface of the substrate 51, it is difficult to form the thin film capacitor element 1011 in the layered structure. Moreover, since the circuit device such as an inductor element cannot be formed near the thin film capacitor element 1011, it is difficult to intend to reduce the size of a composite component having a plurality of circuit devices.
A capacitor element which solves the problems described above is proposed by the inventors (Japanese Patent Application No. 2005-333108). FIG. 37 shows a cross section depicting a capacitor element 611 proposed by the inventors. The capacitor element 611 has a lower conductor 21 which is formed on a substrate 51, a dielectric film 31 which is formed to cover the substrate 51 and the lower conductor 21, an insulating film 33 which is formed on the dielectric film 31, and an upper conductor 623 which is formed over an opening 33b that is formed in the insulating film 33 on the lower conductor 21 and which configures a capacitor element 611 with the lower conductor 21 and the dielectric film 31. The opening 33b has such a square shape that for example, the length of one side is l when the substrate 51 is seen in the normal direction of the substrate surface. The upper conductor 623 has a column shaped conductor part which is formed in the opening 33b, and a lead conductor part which is formed on the insulating film 33 to connect the upper conductor 623 to the other circuit devices such as an inductor element or an external electrode (not shown).
The upper conductor 623 is extended over from the opening 33b to the insulating film 33, which is not formed in the same layer as the lower conductor 21. Thus, even though the film thickness of the dielectric film 31 is thin at the end part of the lower conductor 21 or it is not formed at the end part thereof, the lower conductor 21 is not short circuited with the upper conductor 623. Therefore, the breakdown limit of the withstand voltage value and the insulating properties of the capacitor element 611 are improved, and the quality variations in electronic components having the fabricated capacitor element 611 are suppressed.
In addition, in the capacitor element 611, since the area (the opening diameter) 12 of the opening 33b defines the electrode area of the capacitor element 611, the capacitance value is not varied even though the position of forming the upper conductor 623 is shifted. Therefore, the capacitance value of the capacitor element 611 can be obtained highly accurately. In addition, when the insulating film 33 is thickened, the parasitic inductance and the stray capacitance generated between the lead conductors of the upper conductor 623 and the lower conductor 21 are decreased. Therefore, the capacitance value of the capacitor element 11 can be made more accurately.
In addition, since it is unnecessary to thicken the film thickness of the dielectric film 31 in order to prevent a short circuit between the lower conductor 21 and the upper conductor 623, the film thickness of the dielectric film 31 can be made one tenth of the film thickness before (2 to 3 (μm)) or below, and the capacitor element 611 of high capacitance can be obtained. In addition, since the sufficient capacitance can be obtained even though the size of the electrode area of the capacitor element 611 is reduced, a reduction in size of the electronic component having the capacitor element 611 can be realized.
In addition, different from the thin film capacitor element 1011 disclosed in Patent Reference 1, since the capacitor element 611 has the structure in which the upper conductor 623 is not faced to the side surface of the lower conductor 21, the parasitic capacitance generated between the side part of the lower conductor 21 and the upper conductor 623 is little varied even though the electronic component 1 is reduced in size. In addition, the insulating film 33 is thickened to a few μm, whereby the parasitic capacitance can be suppressed.
Moreover, different from the thin film capacitor element 1011 disclosed in Patent Reference 1, in the capacitor element 611, since the insulating layer 1033 in a protruded shape toward the substrate surface is not formed and the insulating film 33 is formed almost throughout the surface of the substrate 51, the electronic component having the capacitor element 611 can be easily formed in a super multilayer form. Moreover, since the protruded insulating layer 1033 is not formed in the rim part of the capacitor element 11, the other circuit devices such as an inductor element can be formed near the capacitor element 11. Accordingly, a reduction in size of the electronic component having the capacitor element 611 can be realized.
However, the capacitor element 611 has a problem that when it is further reduced in size where the length 1 of one side of the opening 33b is l=5 (μm), for example, the electrode area cannot be formed highly precisely, and the capacitance value cannot be obtained highly accurately.
For example, the insulating film 33 is formed of a photosensitive resin (photoresist). When a photosensitive resin is used for a material for the insulating film 33, the insulating film 33 is formed and then the insulating film 33 is exposed and developed to form the opening 33b. In addition, after the opening 33b is formed, the insulating film 33 is post baked to remove a photosensitive group and an organic solvent in the insulating film 33. Accordingly, the insulating film 33 excellent in environmental resistance can be formed.
Post bake causes the insulating film 33 to cure and shrink. The insulating film 33 is contracted by cure and shrinkage, and the area of the opening 33b is increased. However, an increase in the area of the opening 33b caused by cure and shrinkage is varied for every product. Thus, variations occur in the area of the upper conductor 623 formed in the opening 33b. On the other hand, in order to suppress the parasitic capacitance generated between the side part of the lower conductor 21 and the upper conductor 623, it is necessary to thicken the insulating film 33 to a few μm. The amount of cure and shrinkage of the insulating film 33 is more increased as the insulating film 33 is thicker. In addition, the area of the opening 33b is more decreased as the capacitor element 611 is more reduced in size. Therefore, when the capacitor element 611 is reduced in size, the variations in the area of the opening 33b caused by cure and shrinkage greatly affect the accuracy of the area of the opening 33b. Thus, the capacitor element 611 has problems that when it is reduced in size, the electrode area cannot be formed highly precisely and the capacitance value cannot be obtained highly accurately.
As the properties of the material for forming the insulating film 33 which affects the accuracy of the capacitance value of the capacitor element 611, there are hygroscopic properties and workability in addition to cure and shrinkage. In addition, methods of forming the opening 33b, such as photolithography, laser and plasma, also affect the accuracy of the capacitance value of the capacitor element 611. The same problem arises when photosensitive polyimides, photosensitive epoxy resins and photosensitive benzcyclobutene are used for the material of forming the insulating film 33.
It is possible to use inorganic materials for the material of forming the insulating film 33. When an inorganic material is used, the accuracy of the area of the opening 33b is relatively highly accurate as compared with the case in which a photosensitive resin is used. However, a quite long deposition time is required for forming an inorganic insulating film having a thickness of a few μm using a vapor phase process such as sputtering, and etching for forming the opening 33b takes a long time as well. Therefore, using an inorganic material for the material of forming the insulating film 33 arises another problem that the electronic component having the capacitor element 611 needs more costs than the case of using an organic material.
There is also a method of forming the column shaped conductor part of the upper conductor 623 by etching (subtractive process). However, generally, the accuracy of the shape of the conductor is more dropped as the conductor is formed thicker. Since it is necessary to thicken the insulating film 33 to a few μm, it is also necessary to thicken the column shaped conductor part of the upper conductor 623. Therefore, even though the column shaped conductor part of the upper conductor 623 is formed by etching, the capacitor element 611 has problems that the electrode area cannot be formed highly precisely and the capacitance value cannot be obtained highly accurately.
In addition, as shown in FIG. 37, the insulating film 33 around the opening 33b has a tapered shape. The insulating film 33 at the tip end part in a tapered shape indicated by circle A in FIG. 37 is thin, and functions as the dielectric film of the capacitor element 611 along with the dielectric film 31 directly formed thereunder. However, since the area of the opening 33b as well as the tapered shape of the insulating film 33 have variations, the film thickness of the tip end part in a tapered shape and the area of the opening 33b are varied. Therefore, a problem arises that the variations in tapered shape also affects the capacitance value of the capacitor element 611.
In addition, the insulating film 33 at the tip end part in a tapered shape is thin, and hardly has the insulating properties. Moreover, the dielectric film 31 on the end part of the lower conductor 21 indicated by B in FIG. 37 might be partially broken. This might cause leakage current to be carried through the insulating film 33 at the tip end part in a tapered shape and the broken portion of the dielectric film 31. When leakage current is carried, the insulating film 33 is damaged to cause a problem that the capacitor element 611 does not function as a capacitor.
FIG. 38 shows a thin film capacitor 811 disclosed in Patent Reference 2. As shown in FIG. 38, the thin film capacitor 811 is configured to in turn form a lower electrode layer 821, a dielectric layer 831, a first upper electrode layer 823, and a second upper electrode layer 825 on an insulating substrate 851, having a thickness of 0.005 (μm)≦t1′≦1 (μm), 2×t1′≦t2≦10 (μm) where the thickness of the first upper electrode layer 823 is t1′, and the thickness of the second upper electrode layer 825 is t2′.
The first upper electrode layer 823 serves as a contact layer to obtain sufficient adhesion properties with the dielectric layer 831 working as the upper electrode layer as well as serves as a role to decide the thin film capacitance value of the capacitor by the dimensions (area) of this layer. The second upper electrode layer 825 reduces the conduction resistance of the upper electrode as the main conductor of the upper electrode of the thin film capacitor 811, which has excellent bonding properties for wire bonding and ribbon bonding and soldering properties for a solder.
The thin film capacitor 811 has the upper electrode layer in the layered structure of the first upper electrode layer 823 on the dielectric layer 831 side and the second upper electrode layer 825 formed thereon, in which the thickness t1′ of the first upper electrode layer 823 is reduced to 0.005 to 1 (μm) and the thickness t2′ of the second upper electrode layer 825 is thickened to 2×t1′ to 10 (μm). Thus, since side etching does not occur in the first upper electrode layer 823 as before, the variations in the dimensions can be eliminated, and the counter electrode area can be controlled accurately, whereby the occurrence of variations in the capacitance value can be removed. In addition, since the second upper electrode layer 825 has sufficient thickness, it can be provided with excellent wire bonding properties and low conduction resistance which are considered to be necessary for the upper electrode layer. Consequently, a small sized, highly accurate thin film capacitor 811 can be provided which has very small variations in the capacitance value.
For methods of forming the second upper electrode layer 825, for example, such a method that a metal film such as titanium, tantalum, or nickel-chrome to be the first upper electrode layer 823 and a metal film such as copper, gold, or aluminum to be the second upper electrode layer 825 are deposited on the substrate having layers up to the dielectric layer 831 formed in a predetermined thickness by vapor deposition and sputtering.
Subsequently, a photoresist is formed in a desired pattern shape corresponding to the second upper metal film 825 on the surface of the metal film to be the second upper metal film 825 by photolithographic technique, the photoresist is used as a mask for pattern etching using an etching solution matched with the second upper metal film 825 (for example, ammonium persulfate aqueous solution for copper), and the second upper electrode layer 825 in a predetermined shape and dimensions is formed.
However, the thin film capacitor 811 disclosed in Patent Reference 2 has a problem that it cannot be formed in one piece with the other circuit devices such as an inductor element and a resistance element and it cannot be adapted to a composite component. In addition, the thin film capacitor 811 has a problem that it is difficult to form the thin film capacitor 811 to have a super multilayer form by laminating the dielectric layer 831, the first upper electrode layer 823 and the second upper electrode layer 825 on the second upper electrode layer 825.
In addition, in the thin film capacitor 811, it is likely to etch the first upper electrode layer 823 as well in pattern etching the second upper metal film 825. Therefore, the thin film capacitor 811 has problems that the first upper electrode layer 823 cannot be formed in a desired shape and dimensions and that the accuracy of the counter area is not highly accurate.    Patent Reference 1: JP-A-2002-25854    Patent Reference 2: JP-A-10-135077    Patent Reference 3: JP-A-2002-33559    Patent Reference 4: JP-A-2003-17366    Patent Reference 5: Japanese Patent No. 3193973